Methods of manufacturing electronic structures

ABSTRACT

A structure is disclosed, comprising: a first field effect transistor, FET, comprising a first source terminal, a first drain terminal, a first layer or body of semiconductive material arranged to provide a first semiconductive channel connecting the first source terminal to the first drain terminal, and a gate terminal arranged with respect to the first semiconductive channel such that a conductivity of the first semiconductive channel may be controlled by application of a voltage to the gate terminal; and a second FET comprising a second source terminal, a second drain terminal, a second layer or body of semiconductive material arranged to provide a second semiconductive channel connecting the second source terminal to the second drain terminal, and the gate terminal, the second conductive channel being arranged with respect to the gate terminal such that a conductivity of the second channel may be controlled by application of a voltage to the gate terminal. Methods of manufacturing such structures are also disclosed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national stage application under 35 U.S.C. 371 ofPCT Application No. PCT/GB2018/050805, having an international filingdate of 27 Mar. 2018, which designated the United States, which PCTapplication claimed the benefit of Great Britain Application No.1705270.5, filed 31 Mar. 2017, each of which are incorporated herein byreference in their entirety.

FIELD OF THE INVENTION

The present invention relates to electronic structures comprising twofield effect transistors, FETs, and more particularly, although notexclusively, to structures comprising complementary and symmetricalpairs of P-type and N-type semiconductor FETs.

BACKGROUND TO THE INVENTION

Complementary metal oxide semiconductor (Cmos) is a well-knowntechnology for constructing integrated circuits, and typically usescomplementary and symmetrical pairs of P-type and N-type metal oxidesemiconductor FETs (MOSFETs) for logic functions.

Although the implementation of CMOS technology on conventional siliconwafers is well-established, implementation of CMOS technology oranalogous technology utilising complementary pairs of P-type and N-typeFETs in different applications, such as printed and/or flexibleelectronic circuits is problematic and non-trivial.

SUMMARY OF THE INVENTION

Certain aspects and embodiments of the present invention aim to produceelectronic structures comprising two FETs, for example complementarypairs of N-type and P-type FETs, and corresponding methods ofmanufacture which are suitable for implementation and incorporation inprinted and/or flexible electronic circuits.

A first aspect of the invention provides a structure (which may also bereferred to as an electronic structure) comprising:

-   -   a first field effect transistor, FET, comprising a first source        terminal, a first drain terminal, a first layer or body of        semiconductive material arranged to provide a first        semiconductive channel connecting the first source terminal to        the first drain terminal, and a gate terminal arranged with        respect to (e.g. over) the first semiconductive channel such        that a conductivity of the first semiconductive channel may be        controlled by application of a voltage to the gate terminal; and    -   a second FET comprising a second source terminal, a second drain        terminal, a second layer or body of semiconductive material        arranged to provide a second semiconductive channel connecting        the second source terminal to the second drain terminal, and        said gate terminal, the second conductive channel being arranged        with respect to (e.g. over) said gate terminal such that a        conductivity of the second channel may be controlled by        application of a voltage to the gate terminal (whereby        application of a voltage to the gate terminal may control (e.g.        simultaneously) conductivities of both the first and second        channels).

In certain embodiments the first layer or body of semiconductivematerial comprises a first semiconductive material and the second layeror body of semiconductive material comprises a second semiconductivematerial, different from said first semiconductive material.

In certain embodiments one of the first and second semiconductivematerials is an n-type semiconductor, and the other one of the first andsecond semiconductive materials is a p-type semiconductor.

In certain embodiments the first layer or body of semiconductivematerial is arranged to overlap at least one of the first source anddrain terminals.

In certain embodiments the first layer or body of semiconductivematerial is arranged to overlap both of the first source and drainterminals.

In certain embodiments the first layer or body of semiconductivematerial is arranged not to overlap either of the first source and drainterminals.

In certain embodiments the first source and drain terminals are formedover the first layer or body of semiconductive material.

In certain embodiments the first layer or body of semiconductivematerial, the gate terminal, and the second layer or body ofsemiconductive material are arranged with respect to each other in astack configuration (e.g. a vertical stack).

In certain embodiments the first layer or body of semiconductivematerial, the gate terminal, and the second layer or body ofsemiconductive material are stacked in a nominal vertical direction.

In certain embodiments the first layer or body of semiconductivematerial, the gate terminal, and the second layer or body ofsemiconductive material have the same area as one another.

In certain embodiments the first layer or body of semiconductivematerial, the gate terminal, and the second layer or body ofsemiconductive material are aligned (e.g. vertically aligned) with oneanother.

In certain embodiments the gate terminal is substantially planar, andthe first layer or body of semiconductive material and the second layeror body of semiconductive material are arranged respectively below andabove the gate terminal, spaced from the gate terminal in a directionnormal to the plane of the gate terminal.

In certain embodiments the first layer or body of semiconductivematerial, the gate terminal, and the second layer or body ofsemiconductive material each have the same projection onto the plane ofthe gate terminal.

In certain embodiments the first layer or body of semiconductivematerial and the gate terminal each have the same projection onto theplane of the gate terminal, and the second layer or body ofsemiconductive material has a different projection onto the plane of thegate terminal.

In certain embodiments said projection of the first layer or body ofsemiconductive material and the gate terminal is larger than saidprojection of the second layer or body of semiconductive material.

In certain embodiments the first FET comprises a first layer or body ofdielectric material separating the gate from the first layer or body ofsemiconductive material, and the second FET comprises a second layer orbody of dielectric material separating the gate from the second layer orbody of semiconductive material.

In certain embodiments the first and second layers or bodies ofdielectric material are aligned with the first and second layers orbodies of semiconductive material in a stack configuration.

In certain embodiments the structure further comprises at least onefurther layer or body of dielectric material arranged between (i.e. toseparate) the first source terminal and the second source terminal, andbetween (i.e. to separate) the first drain terminal and the second drainterminal.

In certain embodiments the structure further comprises at least onefurther layer or body of dielectric material arranged to separate saidterminals of the first FET from said terminals of the second FET.

In certain embodiments the second source terminal and the second drainterminal each comprise a respective via extending through the at leastone further layer or body of dielectric material to contact said secondlayer or body of semiconductive material.

In certain embodiments said at least one further layer or body ofdielectric material is arranged to surround a stack comprising the gateterminal and the first and second layers or bodies of semiconductivematerial.

In certain embodiments the structure further comprises at least onefurther layer or body of dielectric material formed over the secondlayer or body of semiconductive material, wherein the second sourceterminal and the second drain terminal each comprise a respective viaextending through the or each further layer or body of dielectricmaterial to contact said second layer or body of semiconductivematerial.

In certain embodiments said vias are positioned over respective portionsof the first source and first drain terminals.

In certain embodiments said vias are arranged over the firstsemiconductive channel, and do not overlap either of the first sourceand first drain terminals.

In certain embodiments the structure further comprises a second gateterminal arranged with respect to the second layer or body ofsemiconductive material and to which a voltage may be applied to controlconductivity of the second semiconductive channel.

In certain embodiments said second gate is arranged above the secondsemiconductive channel (e.g. between the second source and drainterminals).

In certain embodiments the second gate is separated from the secondlayer or body of semiconductive material by at least one layer or bodyof diecectric material.

In certain embodiments the structure further comprises a supportarranged to directly support the first semiconductive channel, andoptionally the first source and drain terminals

In certain embodiments the support comprises a substrate, and optionallya passivation layer formed on the substrate.

Another aspect provides a method of manufacturing a structure(electronic structure) comprising a first FET and a second FET, themethod comprising:

-   -   providing a support;    -   forming a first layer or body of conductive material on the        support;    -   patterning the first layer or body of conductive material to        define a first source terminal, a first drain terminal, and a        first gap separating the first source terminal and the first        drain terminal;    -   forming a first layer or body of semiconductive material        covering the first source and first drain terminals and filling        the gap so as to provide a first semiconductive channel        connecting the first source terminal to the first drain        terminal;    -   forming a first layer or body of dielectric material over the        first layer or body of semiconductive material;    -   forming a layer or body of conductive (gate) material over the        first layer or body of dielectric material;    -   forming a second layer or body of dielectric material over the        layer or body of conductive (gate) material;    -   forming a second layer or body of semiconductive material over        the second layer or body of dielectric material;    -   patterning the first and second layers or bodies of        semiconductive material, the first and second layers or bodies        of dielectric material, and said layer or body of conductive        (gate) material to uncover (expose) portions of the first source        and first drain terminals and produce a stack comprising the        first semiconductive channel, a portion of the first layer or        body of dielectric material over said first channel, a portion        of the layer or body of conductive (gate) material over said        first channel, a portion of the layer or body of second        dielectric material over said first channel, and a portion of        the second layer or body of semiconductive material over the        first channel;    -   forming at least one further layer or body of dielectric        material over the stack to cover the stack and said uncovered        portions of the first source and drain terminals;    -   patterning the at least one further layer or body of dielectric        material to form first and second windows through the at least        one further layer or body of dielectric material to said portion        of the second layer or body of semiconductive material; and    -   forming a second source terminal comprising conductive material        at least partially filling the first window, and a second drain        terminal comprising conductive material at least partially        filling the second window, such that said portion of the second        layer or body of semiconductive material provides a second        semiconductive channel, connecting the second source terminal to        the second drain terminal,    -   whereby the first FET comprises the first source terminal, the        first drain terminal, the first channel, and said portion of the        layer or body of conductive (gate) material, the second FET        comprises the second source terminal, the second drain terminal,        the second channel, and said portion of the layer or body of        conductive (gate) material.

In certain embodiments said stack overlaps at least one of the firstsource and first drain terminals.

In certain embodiments said stack overlaps both of the first source andfirst drain terminals.

In certain embodiments said first window is positioned above a portionof the first source terminal overlapped by the stack and said secondwindow is positioned above a portion of the first drain terminaloverlapped by the stack.

In certain embodiments said stack does not overlap either the firstsource or the first drain terminal.

Another aspect provides a method of manufacturing a structure(electronic structure) comprising a first FET and a second FET, themethod comprising:

-   -   providing a support;    -   forming a first layer or body of conductive material on the        support;    -   patterning the first layer or body of conductive material to        define a first source terminal, a first drain terminal, and a        first gap separating the first source terminal and the first        drain terminal;    -   forming a first layer or body of semiconductive material        covering the first source and first drain terminals and filling        the gap so as to provide a first semiconductive channel        connecting the first source terminal to the first drain        terminal;    -   forming a first layer or body of dielectric material over the        first layer or body of semiconductive material;    -   forming a layer or body of conductive (gate) material over the        first layer or body of dielectric material;    -   patterning the first layer or body of semiconductive material,        the first layer or body of dielectric material, and said layer        or body of conductive (gate) material to uncover (expose) at        least portions of the first source and first drain terminals and        produce a first stack comprising the first semiconductive        channel, a portion of the first layer or body of dielectric        material over said first channel, and a portion of the layer or        body of conductive (gate) material over said first channel;    -   forming a second layer or body of dielectric material over the        first stack and uncovered portions of the first source and first        drain terminals;    -   forming a second layer or body of semiconductive material over        the second layer or body of dielectric material;    -   patterning the second layer or body of semiconductive material        and the second layer or body of dielectric material to uncover        (expose) at least portions of the first source and first drain        terminals and produce a second stack comprising the first        semiconductive channel, said portion of the first layer or body        of dielectric material over said first channel, said portion of        the layer or body of conductive (gate) material over said first        channel, a portion of the layer or body of second dielectric        material over said first channel, and a portion of the second        layer or body of semiconductive material over the first channel;    -   forming at least one further layer or body of dielectric        material over the second stack to cover the second stack and        said uncovered portions of the first source and drain terminals        (not covered by the second stack);    -   patterning the at least one further layer or body of dielectric        material to form first and second windows through the at least        one further layer or body of dielectric material to said portion        of the second layer or body of semiconductive material;    -   forming a second source terminal comprising conductive material        at least partially filling the first window, and a second drain        terminal comprising conductive material at least partially        filling the second window, such that said portion of the second        layer or body of semiconductive material provides a second        semiconductive channel, connecting the second source terminal to        the second drain terminal,    -   whereby the first FET comprises the first source terminal, the        first drain terminal, the first channel, and said portion of the        layer or body of conductive (gate) material, the second FET        comprises the second source terminal, the second drain terminal,        the second channel, and said portion of the layer or body of        conductive (gate) material.

In certain embodiments said patterning to uncover (expose) at leastportions of the first source and first drain terminals and produce saidfirst stack comprises forming a layer of photoresist over said layers tobe patterned, exposing the structure from below with electromagneticradiation such that the first source and first drain terminals shieldportions of the photoresist from said radiation and a portion of thephotoresist above the first semiconductive channel is exposed,processing the photoresist to leave the exposed portion and remove theunexposed portions, removing portions of the layers to be patterned thatwere beneath the unexposed portions of photoresist, and then removingthe exposed portion of photoresist from the top of the first stack.

In certain embodiments said patterning of the at least one further layeror body of dielectric material to form said first and second windowscomprises:

-   -   forming a layer or body of photoresist on the at least one        further layer;    -   exposing the photoresist to radiation through a mask arranged to        leave portions unexposed and expose a portion over the second        semiconductive channel;    -   processing the photoresist to reduce a solubility of the exposed        portion (e.g. cross-link the exposed portion);    -   exposing the structure to radiation from below such that the        first electrodes shield portions of the photoresist and further        portions are reverse exposed;    -   processing the photoresist to remove the reverse exposed        portions and form windows through the photoresist;

removing material of the at least one further layer through said windowsin the photoresist layer to form said first window and said secondwindow; and

removing remaining photoresist material.

In certain embodiments said second stack does not overlap either thefirst source or the first drain terminal.

Another aspect provides a method of manufacturing a structure(electronic structure) comprising a first FET and a second FET, themethod comprising:

-   -   providing a support;    -   forming a first layer or body of conductive material on the        support;    -   patterning the first layer or body of conductive material to        define a first source terminal, a first drain terminal, and a        first gap separating the first source terminal and the first        drain terminal;    -   forming a first layer or body of semiconductive material        covering the first source and first drain terminals and filling        the gap so as to provide a first semiconductive channel        connecting the first source terminal to the first drain        terminal;    -   forming a first layer or body of dielectric material over the        first layer or body of semiconductive material;    -   forming a layer or body of conductive (gate) material over the        first layer or body of dielectric material;    -   forming a second layer or body of dielectric material over the        layer or body of conductive (gate) material;    -   forming a second layer or body of semiconductive material over        the second layer or body of dielectric material;    -   patterning the first and second layers or bodies of        semiconductive material, the first and second layers or bodies        of dielectric material, and said layer or body of conductive        (gate) material to uncover (expose) at least portions of the        first source and first drain terminals and produce a stack        comprising the first semiconductive channel, a portion of the        first layer or body of dielectric material over said first        channel, a portion of the layer or body of conductive (gate)        material over said first channel, a portion of the layer or body        of second dielectric material over said first channel, and a        portion of the second layer or body of semiconductive material        over the first channel;    -   forming at least one further layer or body of dielectric        material over the stack to cover the stack and said uncovered        portions of the first source and drain terminals;    -   patterning the at least one further layer or body of dielectric        material to form first and second windows through the at least        one further layer or body of dielectric material to said portion        of the second layer or body of semiconductive material;    -   forming a second source terminal comprising conductive material        at least partially filling the first window, and a second drain        terminal comprising conductive material at least partially        filling the second window, such that said portion of the second        layer or body of semiconductive material provides a second        semiconductive channel, connecting the second source terminal to        the second drain terminal,    -   whereby the first FET comprises the first source terminal, the        first drain terminal, the first channel, and said portion of the        layer or body of conductive (gate) material, the second FET        comprises the second source terminal, the second drain terminal,        the second channel, and said portion of the layer or body of        conductive (gate) material.

In certain embodiments said patterning to uncover (expose) at leastportions of the first source and first drain terminals and produce saidstack comprises forming a layer of photoresist over said layers to bepatterned, exposing the structure from below with electromagneticradiation such that the first source and first drain terminals shieldportions of the photoresist from said radiation, processing thephotoresist to leave the exposed portion and remove the unexposedportions, removing portions of the layers to be patterned that werebeneath the unexposed portions of photoresist, and then removing theexposed portion of photoresist from the top of the stack.

In certain embodiments said patterning of the at least one further layeror body of dielectric material to form said first and second windowscomprises:

-   -   forming a layer or body of photoresist on the at least one        further layer;    -   exposing the photoresist to radiation through a mask arranged to        leave portions unexposed and expose a portion over the second        semiconductive channel;    -   processing the photoresist to reduce a solubility of the exposed        portion (e.g. cross-link the exposed portion);    -   exposing the structure to radiation from below such that the        first electrodes shield portions of the photoresist and further        portions are reverse exposed;    -   processing the photoresist to remove the reverse exposed        portions and form windows through the photoresist;    -   removing material of the at least one further layer through said        windows in the photoresist layer to form said first window and        said second window; and    -   removing remaining photoresist material.

In certain embodiments said stack does not overlap either the firstsource or the first drain terminal.

In certain embodiments said patterning the at least one further layer orbody of dielectric material to form first and second windows furthercomprises forming at least one of a third window down to the gateterminal and a fourth window down to one of the first source terminaland the first drain terminal.

Another aspect provides a method of manufacturing a structure(electronic structure) comprising a first FET and a second FET, themethod comprising:

-   -   providing a support;    -   forming a first source terminal, a first drain terminal, and a        first layer or body of semiconductive material supported on (by)        the support, the first layer or body of semiconductive material        providing a first semiconductive channel connecting the first        source terminal to the first drain terminal;    -   forming a first layer or body of dielectric material over the        first layer or body of semiconductive material;    -   forming a layer or body of conductive (gate) material over the        first layer or body of dielectric material;    -   forming a second layer or body of dielectric material over the        layer or body of conductive (gate) material;    -   forming a second layer or body of semiconductive material over        the second layer or body of dielectric material;    -   patterning the first and second layers or bodies of        semiconductive material, the first and second layers or bodies        of dielectric material, and said layer or body of conductive        (gate) material to uncover (expose) portions of the first source        and first drain terminals and produce a stack comprising the        first semiconductive channel, a portion of the first layer or        body of dielectric material over said first channel, a portion        of the layer or body of conductive (gate) material over said        first channel, a portion of the layer or body of second        dielectric material over said first channel, and a portion of        the second layer or body of semiconductive material over the        first channel;    -   forming at least one further layer or body of dielectric        material over the stack to cover the stack and said uncovered        portions of the first source and drain terminals;    -   patterning the at least one further layer or body of dielectric        material to form first and second windows through the at least        one further layer or body of dielectric material to said portion        of the second layer or body of semiconductive material; and    -   forming a second source terminal comprising conductive material        at least partially filling the first window, and a second drain        terminal comprising conductive material at least partially        filling the second window, such that said portion of the second        layer or body of semiconductive material provides a second        semiconductive channel, connecting the second source terminal to        the second drain terminal,    -   whereby the first FET comprises the first source terminal, the        first drain terminal, the first channel, and said portion of the        layer or body of conductive (gate) material, the second FET        comprises the second source terminal, the second drain terminal,        the second channel, and said portion of the layer or body of        conductive (gate) material.

Another aspect provides an electronic circuit comprising a structure inaccordance with any other aspect or embodiment.

Further aspects and embodiments of the invention, and their associatedadvantages and the technical problems they address/solve at least partlywill be appreciated from the following detailed description of theaccompanying figures, of which

FIGS. 1-5 illustrate steps in a method of producing an electronicstructure in accordance with a first aspect of the invention;

FIG. 5 illustrates an electronic structure embodying an aspect of theinvention;

FIGS. 6-11 illustrate steps in another method embodying an aspect of thepresent invention;

FIG. 11 illustrates an electronic structure embodying another aspect ofthe invention;

FIGS. 12-18 illustrate further steps which may be incorporated incertain methods embodying an aspect of the present invention to produceelectronic structures embodying an aspect of the invention;

FIG. 19 illustrates another electronic structure in accordance with anaspect of the invention;

FIGS. 20-25 illustrate steps in a method embodying an aspect of theinvention and suitable for manufacturing an electronic circuit inaccordance with FIG. 19;

FIGS. 26-30 illustrate steps in another method embodying an aspect ofthe invention;

FIG. 30 illustrates another electronic circuit in accordance with anembodiment of an aspect of the invention;

FIG. 31 illustrates another electronic structure embodying an aspect ofthe present invention; and

FIG. 32 illustrates a patterning method useable in embodiments of theinvention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIGS. 1-5 illustrate steps in a method embodying an aspect of theinvention and resulting in the structure shown in FIG. 5, which itselfis an electronic structure embodying an aspect of the invention.Referring to FIG. 1, the method comprises providing a support 9, whichin this example is a multi-layer structure comprising a substrate 91 anda passivation layer 92 formed on the substrate. The passivation layer 92may be referred to as a bottom passivation layer, as it will sit beneaththe stacked FETs of the resultant structure. This providing of thesupport 9 may comprise sub-steps, such as preparing the substrate, whichmay for example be glass, silicone, plastic, or other suitable materialdepending on application, and which may be flexible in certainembodiments, or rigid. The passivation layer may be formed by depositingit on the substrate surface by any one of a wide variety of knowndeposition techniques. Although the support 9 in FIG. 1 comprisespassivation layer 92, in certain embodiments the passivation layer maybe omitted, so the deposition of a passivation layer is an optionalstep.

Referring now to FIG. 2, the method further comprises forming a firstlayer or body 1 of conductive material on the support 9, and thenpatterning the first layer or body 1 of conductive material to define afirst source terminal 11, a first drain terminal 12, and a first gap 13separating the first source terminal and the first drain terminal. Itwill be appreciated that the terms source terminal and drain terminalare interchangeable in this example, there being no technical orstructural difference between the two terminals in this embodiment. Thefirst layer or body 1 of conductive material may also be referred to aselectrode 1, or a first electrode layer. The formation of the firstlayer or body 1 of conductive material may comprise depositing the firstelectrode layer by one of a number of suitable techniques, for exampleplasma vapour deposition (PVD). Clearly, this is merely one example, andembodiments may utilise other layer-forming or deposition techniquesknown in the art. The patterning of the first layer or body 1 ofconductive material (i.e. the patterning of the first electrode layer)may also be achieved using one of a number of well-known techniques inthe art, for example by lithography and etching.

Referring now to FIG. 3, the method further comprises forming a firstlayer or body 2 of semiconductive material covering the first source andfirst drain terminals 11, 12 and filling the gap 13 so as to provide afirst semiconductive channel 21 connecting the first source terminal 11to the first drain terminal 12. The method also comprises forming afirst layer or body 3 of dielectric material over the semiconductivelayer 2. The method further comprises forming a layer or body 4 ofconductive gate material over the first layer or body of dielectricmaterial 3, forming a second layer or body 5 of dielectric material overthe conductive gate layer 4, and forming a second layer or body 6 ofsemiconductive material over the second layer or body of dielectricmaterial 5. Typically, in methods embodying the invention the layers 2,3, 4, 5, and 6 will initially cover all of the first source terminal 11and first drain terminal 12.

The method then comprises patterning the layers 2-6 to uncover portionsP11 and P12 of the first source 11 and first drain 12 terminals andproduce a stack 62 comprising the first semiconductive channel 21, aportion P3 of the first dielectric layer, a portion P4 of the gatelayer, a portion P5 of the second dielectric layer, and a portion P6 ofthe second semiconductor layer. It will be appreciated that, in thisembodiment, each layer of the stack has the same projection onto anominal horizontal plane, that nominal horizontal plane being generallythe plane of the first electrode layer 1 for example. Thus, the variouscomponents of the stack are stacked in a nominal vertical direction. Inthis example, the portion P2 of the first semiconductor layer remainingafter the patterning step overlaps both the first source terminal 11 andthe first drain terminal 12. Thus, the first semiconductive channel 21is arranged between the terminals 11 and 12, and the first overlappingportion 211 overlaps the first source 11, and a second overlappingportion 212 overlaps the first drain 12. In the figure the firstsemiconductor layer is also labelled as semi 1, the first dielectriclayer is also labelled gate die 1, the gate layer 4 is also labelledgate, the second gate dielectric layer 5 is labelled gate die 2, and thesecond semiconductor layer 6 is also labelled semi 2. The firstsemiconductor layer may be deposited on the underlying structure using avariety of techniques, e.g. PVD. The first gate dielectric layer 2 maybe deposited, or otherwise formed, by a variety of techniques, e.g. PVD.The gate layer may be deposited or otherwise formed by a variety oftechniques, including, for example, PVD. The second gate dielectriclayer 5 may be deposited or otherwise formed by a variety of techniques,including, for example, PVD. The second semiconductor layer may bedeposited or otherwise formed by a variety of techniques, including, forexample, PVD. The patterning of the layers 2-6 (i.e. the patterning ofall layers from semi 2 to semi 1) can again be achieved using a varietyof known techniques, for example lithography and etching.

Referring now to FIG. 4, the method further comprises forming a furtherlayer or body 7 of dielectric material over the stack 62 to cover thestack and the previously uncovered portions P11 and P12 of the firstsource 11 and first drain 12 terminals. This forming of a further layermay take the form of depositing a passivation dielectric material, e.g.parylene. The method further comprises patterning the further layer orbody 7 of dielectric material to form first 71 and second 72 windowsthrough the further layer or body of dielectric material 7 to the stackportion P6 of the second semiconductor layer 6. This patterning of thefurther layer to form the windows may also be referred to as patterningthe passivation dielectric, and may be achieved using a variety of knowntechniques, including, for example, lithography and etching.

Then, referring to FIG. 5, the method comprises forming a second sourceterminal 81 comprising conductive material 811 at least partiallyfilling the first window, and a second drain terminal 82 comprisingconductive material 812 at least partially filling the second window 72,such that the portion P6 of the second semiconductive layer 6 provides asecond semiconductive channel 61 connecting the second source terminal81 to the second drain terminal 82. The formation of the second sourceand drain terminals 81, 82 may comprise depositing a second electrode orelectrode layer (electrode 2) (or, in other words, forming a layer orbody of conductive material 8, for example by a variety of techniques,including PVD, and then patterning the second electrode layer 8 toremove a portion of that layer over the central portion of thepassivation layer 730, so as to produce separate electrodes 81 and 82.The patterning of the second electrode layer 8 may be achieved using avariety of techniques, including, for example, lithography and etching.

The electronic structure resulting from the method, and illustrated inFIG. 5, is an electronic structure embodying the invention. It comprisesa first FET comprising first source terminal 11, first drain terminal12, first semiconductive channel 21, and gate P4 to which avoltage/potential may be applied to control conductivity of the channel21. It also comprises a second FET comprising second source terminal 81,second drain terminal 82, second semiconductive channel 61, and the samegate P4 as the first FET. Thus, the two FETs are stacked and verticallyaligned. In certain embodiments, the semiconductive material of firstchannel 21 may be N or P-type, and the semiconductive material of thesecond channel 61 may be of the opposite type. Thus, in certainembodiments the structure may comprise a complementary and symmetricalpair of N-type and P-type devices sharing a common gate P4.

The passivation dielectric material 7 may, in certain embodiments, below-k material, and in alternative embodiments may be high-k material,depending on particular requirements.

It will be appreciated that the above steps described with reference toFIG. 3 can be split into multiple individual steps. Also, although themethod is illustrated as including formation of bottom electrodes 11 and12 and then forming of the first semiconductor layer 2 on top of thoseelectrodes, alternative embodiments can utilise a top-contact design, inother words the first terminals 11 and 12 may be formed on top of apreviously formed or deposited layer of semiconductive material 2, andthen the further layers 3-6 of the stack 62 may be built up on top ofthose electrodes.

It will be appreciated that advantages provided by the structure of FIG.5 include the advantage that the vertical stack results in a smallercircuit footprint, leading to higher yield and/or more dense circuitsbeing achievable. It will also be appreciated that a substantial benefitof the method illustrated by FIGS. 1-5 are that the technique avoidsprocessing on semiconductor/dielectric interfaces, resulting in reducednumbers of defects and/or better performance of the resultanttransistors and circuits in which they are incorporated. In other words,the method illustrated by FIGS. 1-5 results in a structure comprisingtwo stacked FETs, with their channel conductivities controlled by asingle, common gate (sandwiched between them). Thesemiconductor/dielectric interfaces, after formation, are undisturbed.No subsequent processing is performed on them. They are therefore low indefects. The source and drain electrodes are generally on the oppositeside of the semiconductor layers to the gate dielectrics, and are formedin the manner that does not require any disturbance or processing of thesemiconductor/dielectric interfaces once formed.

It will also be appreciated that the structure shown in FIG. 5 alsoprovides the advantage of reducing parasitic capacitances between theelectrodes and the gate. This is achieved, at least in part, by thepresence of the passivation dielectric material. Also, it will beappreciated that the portions 811 and 812 of the second source and drainelectrodes which fill the windows 71, 72 through the passivation layercan be regarded as conductive vias connecting the portion P6 of thesecond semiconductor layer to the remaining portions of the secondsource and drain electrodes 81, 82. Thus, the passivation materialseparates the bulk of the second source and drain electrodes 81 and 82from the gate P5, reducing parasitic capacitances between them.

Referring now to FIGS. 6-11, these illustrate steps in another methodembodying an aspect of the invention and suitable for producing anelectronic structure embodying an aspect of the invention, as shown inFIG. 11. Referring first to FIG. 6, the method again comprises providinga support 9. Moving on to FIG. 7, electrodes 11 and 12 are then formedon the support by any suitable technique, for example by PVD followed bypatterning such as lithography and etching. Referring then to FIG. 8,first semiconductor, first gate dielectric, and gate layers or bodies(2, 3, 4 respectively) are formed on the structure of FIG. 7 by suitabletechniques (e.g. by PVD) and then patterned to produce a first stack 621comprising portions P2, P3 and P4 of those layers 2, 3, and 4respectively. In this example, it will be appreciated that thepatterning of those layers 2, 3, and 4 have been performed such that thefirst stack 621, and indeed its lowermost layer which is portion P2 ofthe first semiconductor layer 2, does not overlap either the electrodes11, 12. Advantageously, this reduces parasitic capacitances. In certainembodiments, this accurate alignment, to avoid overlap between the gateP4 and the first electrodes 11, 12 may be achieved using a technique asillustrated in FIG. 32. Referring to FIG. 32, the layers to be patterned(in this example layers 2, 3, and 4) are shown, formed over theelectrode structure comprising electrodes 11 and 12, supported by thesupport structure 9. At the stage illustrated in FIG. 32 the layers areas yet unpatterned. A layer of resist material 100 has been formed ontop of the layers to be patterned. To pattern the layers, the structureis illuminated from underneath (in the figure) with radiation ofsuitable wave length (e.g. UV radiation) taking into account theproperties of the resist material 100. The support 9 and layers 2, 3 and4 in this example are substantially transparent to the radiation,whereas electrodes 11 and 12 are opaque. The electrodes 11 and 12 thusact as an in-situ photo mask, such that a central portion 101 of thephoto resist layer is exposed to the radiation, whereas portions 102above the electrodes 11, 12 are unexposed. After this exposure, thestructure is processed and developed using techniques well-known in theart to first remove the unexposed portions 102 of the photo resist layer100, then remove the underlying portions of the layers 2, 3, and 4, andthen the remaining exposed portion 101 of the layer 100 is removed,leaving the aligned stack comprising the central portions P2, P3 and P4of the patterned layers.

Referring now to FIG. 9, after forming the aligned first stack 621, themethod further comprises forming the second gate dielectric layer 5 andsecond semiconductor layer 6 on top of the stack (e.g. by PVD) andpatterning both of those layers 5 and 6 by suitable techniques (e.g. bylithography and etching) to produce a resultant aligned second stack 622comprising those portions P2-P6 of the various layers formed on theelectrode/support underlying structure. It will be appreciated that if areverse side illumination technique is used to produce the aligned firststack 621, then the support 9 and layers 2-4 must each be at leastsubstantially transparent to the radiation being used to expose thephoto resist. However, if the reverse exposure technique is only used topattern those layers 2-4, and not layers 5 and 6, then the choice ofmaterials for layers 5 and 6 becomes wider; they are not required to besubstantially transparent to the UV radiation. Thus, the techniquesillustrated by FIG. 9 are suitable for manufacturing embodiments inwhich layers 5 and 6 are of non-transparent material.

Referring now to FIG. 10, as with the embodiment described withreference to FIG. 4, a passivation dielectric layer or body (e.g. oflow-k material, or of high-k material) is formed over the second stack622 and exposed/uncovered portions of the first electrodes 11 and 12,and this passivation dielectric material may be formed by a variety oftechniques, including deposition. In certain embodiments the passivationdielectric layer may be formed from parylene. Then the passivationdielectric layer is patterned, for example using lithography andetching, to form windows 71 and 72 through to the portion P6 of thesecond semiconductor layer 6. Then, referring to FIG. 11, the secondelectrodes 81 and 82 are formed, each comprising a respective via 811,812 passing through the passivation dielectric material 7 and contactingan upper surface of the portion P6 of the second semiconductor layer 6.The electrodes may be formed by techniques previously described. It willbe appreciated that the second electrodes 81, 82 may be formed by avariety of techniques well-known in the art, for example by lithographyand etching, but can also, in certain embodiments, be produced by aself-aligned technique by repeating rear-side illumination process ifthe gate material is transparent, i.e. if the first electrode layercomprising electrodes 11 and 12 locks UV light but the gate lets the UVthrough to define a window. This window may then be used to defineself-aligned vias within the passivation dielectric into which amaterial to produce the second electrodes 81 and 82 is deposited.Combined with a low-k passivation dielectric this can minimise theimpact of the second electrodes 81, 82 on the gate, thus minimisingparasitics. This self-aligned technique, employing rear-sideillumination, is explained in more detail below with reference to FIGS.12-18.

It will be appreciated that the above-described method of producing astructure in accordance with FIG. 11 provides the advantages of reduceddefects, and smaller circuit footprint. It will also be appreciated thatwhilst the reverse side illumination technique was used to produce aself-aligned first stack 621 of just layers 2, 3 and 4, in alternativeembodiments a similar technique could be used to pattern all of layers2-6. In such embodiments, each of layers 2-6 is required to betransparent to the wavelength being used to interact with the photoresist. Then, rather than patterning layers 2-4 to form a first stackbefore then depositing layers 5 and 6, all of layers 2-6 may bedeposited before patterning. The reverse side illumination technique maythen be used as described with reference to FIG. 32 to produce analigned stack comprising portions P2-P6.

Referring now to FIGS. 12-18, these show how a technique involvingreverse exposure may be used to produce self-aligned electrode viasconnecting to the upper semiconductor layer.

Referring now to FIG. 12, a second aligned stack 622 has been producedas described above, and a passivation layer 7, e.g. of low-k material,has been formed over the stack and the first electrodes 11, 12. A layerof photo resist material 500 has been formed on top of the structure (inthis example on top of an upper surface of the passivation material 7and that layer of photo resist 500 has been exposed to UV radiationthrough a chrome mask 600 having a window 601 positioned over the stackbut having a projection onto the horizontal plane smaller than each ofthe stack layers. This results in essential portion 501 of the photoresist layer 500 being exposed to UV radiation, but portions 502 ofphoto resist remaining unexposed, shielded by the chrome mask 600. Thephoto resist may be formed on the dielectric 7 by a variety oftechniques, including deposition, for example. Thus, the photo resisthas been exposed from the nominal top, and the resultant structure isthen suitably processed (e.g. by baking at an appropriate temperate foran appropriate length of time to cross-link the exposed photo resistmaterial, making it resistant to developer. Then, referring to FIG. 13,the reverse surface is then exposed to UV radiation (in other words thestructure is now exposed to radiation from below (a reverse exposure)).With suitable materials having been used for the various layers, the UVlight is able to pass through each of the layers 2-6 and 7 but is unableto pass through the electrodes 11 and 12. Thus, the first electrodes 11,12 act as in-situ photo masks and shield portions 520 of the photoresist from the radiation. Unshielded portions 510 of the photo resistlayer are thus reverse exposed to UV radiation. The central cross linkedportion 501 is also exposed to radiation. However, that central portion501 is already cross-linked and does not soften. The reverse exposedportions 510 do soften, however.

Referring now to FIG. 14, in a new step the photo resist material is nowdeveloped and the cross linked and unexposed portions of photo resistremain in place, whereas the reverse exposed portions are removed. Next,as shown in FIG. 15, the structure is further processed to removedielectric material that was located underneath the reverse-exposedportions of photo-resist. A variety of suitable techniques may be usedfor this purpose, for example etching, and this results in the formationof windows 71 and 72 through the passivation layer to the underlyingsemiconductor material. Then, as shown in FIG. 16, the remaining photoresist material may be removed by suitable technique (e.g. by resiststripping), and then a top layer of conductive material may be formedover the remaining passivation material and at least partly filling thewindows 71 and 72 to form conductive vias connecting to the secondsemiconductor layer. Finally, as shown in FIG. 18, the top electrodelayer may be patterned to yield the final structure comprising separatesecond electrodes 81 and 82 as shown in FIG. 18. As mentioned above, theabsence of any overlap between the gate and first electrodes 11, 12 inthe structure of FIG. 18 results in low parasitic capacitances, as doesthe fact that the second electrodes 81 and 82 are separated from thegate material by passivation dielectric 7 and connect to the uppersemiconductor layer only through the vias 811, 812.

Referring now to FIG. 19, this illustrates another structure (electronicstructure) embodying an aspect of the present invention. This structureis similar to the structure illustrated in FIG. 5 and again comprisesfirst and second FETs arranged in a vertically stacked configuration,and sharing a common gate P4. However, in this embodiment the secondgate dielectric portion PP5 and second semiconductor layer portion PP6(which provides the second semiconductive channel 61) are not exactlyaligned with the underlying gate P4, first gate dielectric P3, and firstportion of semiconductor P2. Instead, the second semiconductor portionPP6 and second gate dielectric PP5 have the same footprints as oneanother (i.e. projections onto a nominal horizontal plane) but thatfootprint or projection is smaller than that of the gate and first gatedielectric. In other words, the arrangement is such that there is atleast one portion of the gate P4 that is not covered by the second gatedielectric PP5 and second semiconductor layer PP6. Advantageously, thatdifference in size or extent of the gate from the overlying layers PP5and PP6 of the stack enables a gate via 83 to be provided, forming aconnection through the passivation layer 7 and connecting to the gate.Similarly, at least a portion of the first electrode 11 is not coveredby the gate P4, and a further via 84 is formed through the passivationlayer 7, to make electrical connection to the terminal 11.

Generally, the structure shown in FIG. 19 is manufactured using a methodsimilar to the illustrated with reference to FIGS. 1-5. A difference,however, is that after depositing the gate layer 4, the method does notimmediately proceed to depositing layers 5 and 6. Instead, afterdepositing layer 4, layers 4, 3, and 2 are first patterned so as to havea first extent or footprint over the underlying support. Then, thesecond gate dielectric 5 and second semiconductor layer 6 are deposited,then patterned separately from layers 2, 3 and 4, to produce theillustrated stack structure, that is a stack not having uniform crosssection, footprint, or extent, but instead being stepped. The lowerportion of the stack has a first extent or footprint, and the upperportion of the stack (comprising portions PP5 and PP6 has a smallerextent (i.e. a reduced footprint). After formation of the steppedstacked structure, the passivation dielectric 7 is formed and thenpatterned to open vias to the second semiconductor portion PP6, the gateP4, and at least one of the first electrodes 11 all at the same time.These vias may then be filled in a single processing step, whereconductive material is deposited inside them and over the passivationlayer 7. That conductive material may then be patterned as appropriate.

A method of producing the structure shown in FIG. 19 will now bedescribed in more detail with reference to FIGS. 20-25.

Referring now to FIG. 20, a support is provided in the same manner, orin a similar manner, as described above. Referring to FIG. 21, a firstconductive layer or body 1 is formed and then patterned to provide firstelectrodes 11 and 12 separated by gap 13. Then, a first semiconductorlayer or body, a first gate dielectric layer or body, and a gateconductor layer 3 are deposited and then patterned, for example, usinglithography and etching, to produce the stacked structure illustrated inFIG. 22, leaving portions of the first electrodes 11, 12 exposed (i.e.uncovered). Then, referring to FIG. 23, a second gate dielectric layer 5is deposited, as is a second semiconductor layer 6, for example usingPVD or any other suitable technique. Then, these layers 5 and 6 arepatterned, again using any suitable technique, for example lithographyand etching, to produce the stepped, stacked structure shown in FIG. 23.Then, referring to FIG. 24, passivation dielectric material 7 isdeposited over the structure shown in FIG. 23 and then patterned (forexample using lithography and etching) to produce windows 71, 72 throughto the second semiconductor portion PP6, a window 73 through to the gateP4, and a further window 74 through to one of the first layer electrodes11. Then, referring to FIG. 25 conductive material is formed, forexample by a deposition technique such as PVD, and then patterned (forexample using lithography and etching, to yield electrodes 81, 82, 83,and 84.

Thus, the technique to manufacture the structure shown in FIG. 25 issimilar to that used to produce the structure shown in FIG. 5, butprovides the additional advantage that it enables via connections to bemade between layers. At the same time, it maintains the quality of thegate dielectric/semiconductor interfaces, and maintains a compactfootprint through vertical stacking.

Referring now to FIG. 30, this illustrates another structure embodyingan aspect of the invention. The structure is similar to that illustratedin FIG. 5 and described above, but has an additional gate 803 (which maybe referred to as a back-gate) formed above the portion of thepassivation dielectric 730 which is formed on top of the secondsemiconductor portion P6. The structure of FIG. 30 may be produced by amethod as illustrated in FIGS. 26-30, starting with provision of asupport or support structure 9 (see FIG. 26), followed by formation ofthe electrodes 11, 12 of the lower FET in the eventual stackedconfiguration. On top of the structure shown in FIG. 27, successivelayers of semiconductor 2, dielectric 3, gate conductor 4, second gatedielectric 5, and second semiconductor 6 may be formed, and thenpatterned by a suitable technique to form the aligned, stacked structureshown in FIG. 28. A passivation dielectric 7 may then be formed andpatterned as shown in FIG. 29. The upper electrode layer 8 may then beformed (for example by deposition, such as PVD) and then patterned todefine separate electrodes 81 and 82 and the optional back-gate 803. Theformation of the stacked structure shown in FIG. 28 may, in alternativeembodiments, be split into multiple stages, such that the patterning ofeach layer above the support 9 and electrodes 11, 12 need notnecessarily be performed at the same time. Advantageously, theadditional gate 803 (or back-gate) can be used to provide additionalcontrol to one or both of the N and P-type devices, for example toadjust threshold voltage. Although the formation of the additional gate803 separate from the electrodes 81 and 82 may be achieved using avariety of conventional techniques, such as lithography and etching,certain embodiments may utilise techniques involving reverse-sideillumination, as described elsewhere in this document, to produceaccurate self-alignment, for example using the first electrode layer(comprising electrodes 11 and 12) as an in-situ photo mask.

Referring now to FIG. 31, this shows another structure embodying theinvention. This structure is similar to that illustrated in FIG. 5 andmay, generally, be produced by similar methods. However, rather thanhaving a single layer 7 of passivation dielectric material, thisembodiment incorporates a first passivation dielectric 7 a (which may,for example, be high-k material), and a second layer or body ofpassivation dielectric material 7 b (e.g. low-k material). It will beappreciated that, after forming the stack of portions P2-P6 on theunderlying electrode and support structure 11, 12, 9, the firstpassivation dielectric material 7 a may be formed over the stack andoptionally the electrodes 11, 12, and then optionally patterned asrequired, to expose/uncover portions of the electrodes 11, 12. Thesecond passivation dielectric 7 b may then be formed over the firstpassivation dielectric 7 a and then patterned to produce windows 71 and72, which are then filled with conductive material to form the vias 811and 812 of the electrodes 81 and 82. Advantageously, the two passivationdielectrics 7 a and 7 b help to minimise parasitic capacitance betweenelectrode 2 (that is electrode defined by portion P6) and a gate P4.This concept of utilising two passivation dielectrics may be applied tothe above-mentioned aspects and embodiments of the invention.

In certain embodiments the substrate comprises at least one material(e.g. in the form of a layer of that material) selected from a listcomprising: glass (rigid or flexible); polymer (e.g. polyethylenenaphthalate or polyethylene terephthalate); polymeric foil; paper;insulator coated metal (e.g. coated stainless-steel); cellulose;parylene; polymethyl methacrylate; polycarbonate, polyvinylalcohol;polyvinyl acetate; polyvinyl pyrrolidone; polyvinylphenol; polyvinylchloride; polystyrene; polyethylene naphthalate; polyethyleneterephthalate; polyamide (e.g. Nylon); poly(hydroxyether); polyurethane;polycarbonate; polysulfone; polyarylate; acrylonitrile butadienestyrene, 1-Methoxy-2-propyl acetate (SU-8), polyhydroxybenzylsilsesquioxane (HSQ), polyimide, Benzocyclobutene (BCB), Al₂O₃,SiO_(x)N_(y), SiO₂, Si₃N₄; UV-curable resin; Nanoimprint resist;photoresist.

A wide variety of techniques may also be used to form the at least onelayer of resist material, and a variety of resist materials may beemployed in different embodiments of the invention. These methods offorming the at least one layer of resist material include coating (spin,dip, blade, bar, spray, slot-die) or extrusion. Suitable resistmaterials include poly hydroxybutyrate, polymethyl methacrylate,polyvinylalcohol, polyvinyl acetate, polyvinyl pyrrolidone,polyvinylphenol, polyvinyl chloride, polystyrene, polyamide (e.g.Nylon), poly(hydroxyether), polyurethane, polycarbonate, polysulfone,polyarylate, acrylonitrile butadiene styrene, polyimide,benzocyclobutene (BCB), photoresist, 1-Methoxy-2-propyl acetate (SU-8),polyhydroxybenzyl silsesquioxane (HSQ), fluorinated polymers e.g. PTFE,uv curable liquid resin (such as those described in U.S. Pat. No.6,284,072), silicone, silioxane, parylene. Commercial imprint resistsare available through companies such as Microchem/Microresist, Shipleyand Nanolithosolution Inc.

A wide variety of semiconductive materials may be used in embodiments ofthe invention, including for example: metal oxides such as zinc oxide,tin oxide, nickel oxide, tin(II) oxide, tin (IV) oxide, cuprous oxide;inorganic semiconductor such as amorphous, microcrystalline ornanocrystalline silicon; binary semiconductors such as gallium arsenide;ternary semiconductors such as InGaAs; quaternary semiconductors such asInGaAsSb; binary metal oxides such as lithium zinc oxide, zinc tinoxide, indium tin oxide, indium zinc oxide; ternary metal oxides such asGaInZnO; metal oxynitrides e.g. Zn_(x)O_(y)N_(z); organic or polymersemiconductors (n- and p-type). Chalcogenide materials may also bedeposited in semiconducting form, including MoS₂, GST. Doping of any ofthese materials may be applied to adjust the properties so that they areperform better as semiconducting materials.

The depositing of dielectric material can be performed using a varietyof techniques, including: vapour deposition (physical e.g. sputter;chemical e.g. PECVD); vacuum deposition (e.g. thermal or e-beamevaporation); coating e.g. spray, spin, slot, die; printing e.g. jet;pulsed-laser deposition (PLD); atomic-layer deposition (ALD).

Dielectric materials suitable for use in embodiments of the inventioninclude the following: benzocyclobutene (BCB); polyimide; polymethylmethacrylate, polybutyl methacrylate, polyethyl methacrylate, polyvinylacetate, polyvinyl pyrrolidone, polyvinylphenol, polyvinylchloride,polystyrene, polyethylene, polyvinyl alcohol, polycarbonate, parylene;inorganic insulator such as silica, silicon nitride, metal oxide (e.g.Al₂O₃, HfO₂, TiO₂, Ta₂O₅, Y₂O₅, ZrO₂), metal phosphates (e.g.Al₂PO_(x)), metal sulphates/sulfites (e.g. HfSO_(x)), metal oxynitrides(e.g. AlO_(x)N_(y)), metal nitride (AlN), silicone, silioxane, SiN_(x)Examples of low-k dielectrics include Cytop, HSQ, parylene. Examples ofhigh-k dielectrics include Ta₂O₅, HfO₂.

The depositing of electrically conductive material can be achieved usinga variety of techniques, including: vapour deposition (physical e.g.sputter; chemical e.g. PECVD); vacuum deposition (e.g. thermal or e-beamevaporation); coating e.g. spray, spin, slot, die; printing e.g. jet;pulsed-laser deposition (PLD); atomic-layer deposition (ALD).

A wide range of materials can be used as the electrically conductivematerial, including for example: metal (e.g. Au, Ag, Ti, Al, Cr, Ni, Cu,Ta, W, Pt, Mo etc.), metal alloys (e.g. MoNi, MoCr, AlSi) transparentconductive oxide (e.g. ITO, AZO, IZO), metal nitrides (e.g. TiN), carbonblack, carbon nanotubes, conducting polymer (e.g. polyaniline,PEDOT:PSS)

Throughout the description and claims of this specification, the words“comprise” and “contain” and variations of them mean “including but notlimited to”, and they are not intended to (and do not) exclude othermoieties, additives, components, integers or steps. Throughout thedescription and claims of this specification, the singular encompassesthe plural unless the context otherwise requires. In particular, wherethe indefinite article is used, the specification is to be understood ascontemplating plurality as well as singularity, unless the contextrequires otherwise.

Features, integers, characteristics, compounds, chemical moieties orgroups described in conjunction with a particular aspect, embodiment orexample of the invention are to be understood to be applicable to anyother aspect, embodiment or example described herein unless incompatibletherewith. All of the features disclosed in this specification(including any accompanying claims, abstract and drawings), and/or allof the steps of any method or process so disclosed, may be combined inany combination, except combinations where at least some of suchfeatures and/or steps are mutually exclusive. The invention is notrestricted to the details of any foregoing embodiments. The inventionextends to any novel one, or any novel combination, of the featuresdisclosed in this specification (including any accompanying claims,abstract and drawings), or to any novel one, or any novel combination,of the steps of any method or process so disclosed.

The reader's attention is directed to all papers and documents which arefiled concurrently with or previous to this specification in connectionwith this application and which are open to public inspection with thisspecification, and the contents of all such papers and documents areincorporated herein by reference.

The invention claimed is:
 1. A method of manufacturing an electronicstructure comprising a first FET and a second FET, the methodcomprising: providing a support; forming a first layer or body ofconductive material on the support; patterning the first layer or bodyof conductive material to define a first source terminal, a first drainterminal, and a first gap separating the first source terminal and thefirst drain terminal; forming a first layer or body of semiconductivematerial covering the first source and first drain terminals and fillingthe gap so as to provide a first semiconductive channel connecting thefirst source terminal to the first drain terminal; forming a first layeror body of dielectric material over the first layer or body ofsemiconductive material; forming a layer or body of conductive materialover the first layer or body of dielectric material; forming a secondlayer or body of dielectric material over the layer or body ofconductive material; forming a second layer or body of semiconductivematerial over the second layer or body of dielectric material;patterning the first and second layers or bodies of semiconductivematerial, the first and second layers or bodies of dielectric material,and said layer or body of conductive material to uncover portions of thefirst source and first drain terminals and produce a stack comprisingthe first semiconductive channel, a portion of the first layer or bodyof dielectric material over said first channel, a portion of the layeror body of conductive material over said first channel, a portion of thelayer or body of second dielectric material over said first channel, anda portion of the second layer or body of semiconductive material overthe first channel; forming at least one further layer or body ofdielectric material over the stack to cover the stack and said uncoveredportions of the first source and drain terminals; patterning the atleast one further layer or body of dielectric material to form first andsecond windows through the at least one further layer or body ofdielectric material to said portion of the second layer or body ofsemiconductive material; and forming a second source terminal comprisingconductive material at least partially filling the first window, and asecond drain terminal comprising conductive material at least partiallyfilling the second window, such that said portion of the second layer orbody of semiconductive material provides a second semiconductivechannel, connecting the second source terminal to the second drainterminal, whereby the first FET comprises the first source terminal, thefirst drain terminal, the first channel, and said portion of the layeror body of conductive material, the second FET comprises the secondsource terminal, the second drain terminal, the second channel, and saidportion of the layer or body of conductive material.
 2. A method inaccordance with claim 1, wherein said stack overlaps at least one of thefirst source and first drain terminals.
 3. A method in accordance withclaim 2, wherein said stack overlaps both of the first source and firstdrain terminals.
 4. A method in accordance with claim 3, wherein saidfirst window is positioned above a portion of the first source terminaloverlapped by the stack and said second window is positioned above aportion of the first drain terminal overlapped by the stack.
 5. A methodin accordance with claim 1, wherein said stack does not overlap eitherthe first source or the first drain terminal.
 6. A method in accordancewith claim 1, wherein said patterning the at least one further layer orbody of dielectric material to form first and second windows furthercomprises forming at least one of a third window down to a gate terminaland a fourth window down to one of the first source terminal and thefirst drain terminal.
 7. A method of manufacturing an electronicstructure comprising a first FET and a second FET, the methodcomprising: providing a support; forming a first layer or body ofconductive material on the support; patterning the first layer or bodyof conductive material to define a first source terminal, a first drainterminal, and a first gap separating the first source terminal and thefirst drain terminal; forming a first layer or body of semiconductivematerial covering the first source and first drain terminals and fillingthe gap so as to provide a first semiconductive channel connecting thefirst source terminal to the first drain terminal; forming a first layeror body of dielectric material over the first layer or body ofsemiconductive material; forming a layer or body of conductive materialover the first layer or body of dielectric material; patterning thefirst layer or body of semiconductive material, the first layer or bodyof dielectric material, and said layer or body of conductive material touncover at least portions of the first source and first drain terminalsand produce a first stack comprising the first semiconductive channel, aportion of the first layer or body of dielectric material over saidfirst channel, and a portion of the layer or body of conductive materialover said first channel; forming a second layer or body of dielectricmaterial over the first stack and uncovered portions of the first sourceand first drain terminals; forming a second layer or body ofsemiconductive material over the second layer or body of dielectricmaterial; patterning the second layer or body of semiconductive materialand the second layer or body of dielectric material to uncover at leastportions of the first source and first drain terminals and produce asecond stack comprising the first semiconductive channel, said portionof the first layer or body of dielectric material over said firstchannel, said portion of the layer or body of conductive material oversaid first channel, a portion of the layer or body of second dielectricmaterial over said first channel, and a portion of the second layer orbody of semiconductive material over the first channel; forming at leastone further layer or body of dielectric material over the second stackto cover the second stack and said uncovered portions of the firstsource and drain terminals; patterning the at least one further layer orbody of dielectric material to form first and second windows through theat least one further layer or body of dielectric material to saidportion of the second layer or body of semiconductive material; forminga second source terminal comprising conductive material at leastpartially filling the first window, and a second drain terminalcomprising conductive material at least partially filling the secondwindow, such that said portion of the second layer or body ofsemiconductive material provides a second semiconductive channel,connecting the second source terminal to the second drain terminal,whereby the first FET comprises the first source terminal, the firstdrain terminal, the first channel, and said portion of the layer or bodyof conductive material, the second FET comprises the second sourceterminal, the second drain terminal, the second channel, and saidportion of the layer or body of conductive material.
 8. A method inaccordance with claim 7, wherein said patterning to uncover at leastportions of the first source and first drain terminals and produce saidfirst stack comprises forming a layer of photoresist over said layers tobe patterned to produce the first stack, exposing the structure frombelow with electromagnetic radiation such that the first source andfirst drain terminals shield portions of the photoresist from saidradiation and a portion of the photoresist above the firstsemiconductive channel is exposed, processing the photoresist to leavethe exposed portion and remove unexposed portions, removing portions ofthe layers to be patterned that were beneath the unexposed portions ofphotoresist, and then removing the exposed portion of photoresist from atop portion of the first stack.
 9. A method in accordance with claim 7,wherein said patterning of the at least one further layer or body ofdielectric material to form said first and second windows comprises:forming a layer or body of photoresist on the at least one furtherlayer; exposing the photoresist to radiation through a mask arranged toleave portions unexposed and expose a portion over the secondsemiconductive channel; processing the photoresist to reduce asolubility of the exposed portion; exposing the structure to radiationfrom below such that first electrodes shield portions of the photoresistand unshielded portions are reverse exposed; processing the photoresistto remove the reverse exposed portions and form windows through thephotoresist; removing material of the at least one further layer throughsaid windows in the photoresist layer to form said first window and saidsecond window; and removing remaining photoresist material.
 10. A methodin accordance with claim 7, wherein said second stack does not overlapeither the first source or the first drain terminal.
 11. A method ofmanufacturing an electronic structure comprising a first FET and asecond FET, the method comprising: providing a support; forming a firstlayer or body of conductive material on the support; patterning thefirst layer or body of conductive material to define a first sourceterminal, a first drain terminal, and a first gap separating the firstsource terminal and the first drain terminal; forming a first layer orbody of semiconductive material covering the first source and firstdrain terminals and filling the gap so as to provide a firstsemiconductive channel connecting the first source terminal to the firstdrain terminal; forming a first layer or body of dielectric materialover the first layer or body of semiconductive material; forming a layeror body of conductive material over the first layer or body ofdielectric material; forming a second layer or body of dielectricmaterial over the layer or body of conductive material; forming a secondlayer or body of semiconductive material over the second layer or bodyof dielectric material; patterning the first and second layers or bodiesof semiconductive material, the first and second layers or bodies ofdielectric material, and said layer or body of conductive material touncover at least portions of the first source and first drain terminalsand produce a stack comprising the first semiconductive channel, aportion of the first layer or body of dielectric material over saidfirst channel, a portion of the layer or body of conductive materialover said first channel, a portion of the layer or body of seconddielectric material over said first channel, and a portion of the secondlayer or body of semiconductive material over the first channel; formingat least one further layer or body of dielectric material over the stackto cover the stack and said uncovered portions of the first source anddrain terminals; patterning the at least one further layer or body ofdielectric material to form first and second windows through the atleast one further layer or body of dielectric material to said portionof the second layer or body of semiconductive material; forming a secondsource terminal comprising conductive material at least partiallyfilling the first window, and a second drain terminal comprisingconductive material at least partially filling the second window, suchthat said portion of the second layer or body of semiconductive materialprovides a second semiconductive channel, connecting the second sourceterminal to the second drain terminal, whereby the first FET comprisesthe first source terminal, the first drain terminal, the first channel,and said portion of the layer or body of conductive material, the secondFET comprises the second source terminal, the second drain terminal, thesecond channel, and said portion of the layer or body of conductivematerial.
 12. A method in accordance with claim 11, wherein saidpatterning to uncover at least portions of the first source and firstdrain terminals and produce said stack comprises forming a layer ofphotoresist over said layers to be patterned to produce the stack,exposing the structure from below with electromagnetic radiation suchthat the first source and first drain terminals shield portions of thephotoresist from said radiation, processing the photoresist to leave theexposed portion and remove unexposed portions, removing portions of thelayers to be patterned that were beneath the unexposed portions ofphotoresist, and then removing the exposed portion of photoresist fromtop of the stack.
 13. A method in accordance with claim 11, wherein saidpatterning of the at least one further layer or body of dielectricmaterial to form said first and second windows comprises: forming alayer or body of photoresist on the at least one further layer; exposingthe photoresist to radiation through a mask arranged to leave portionsunexposed and expose a portion over the second semiconductive channel;processing the photoresist to reduce a solubility of the exposedportion; exposing the structure to radiation from below such that firstelectrodes shield portions of the photoresist and unshielded portionsare reverse exposed; processing the photoresist to remove the reverseexposed portions and form windows through the photoresist; removingmaterial of the at least one further layer through said windows in thephotoresist layer to form said first window and said second window; andremoving remaining photoresist material.
 14. A method in accordance withclaim 11, wherein said stack does not overlap either the first source orthe first drain terminal.
 15. A method of manufacturing an electronicstructure comprising a first FET and a second FET, the methodcomprising: providing a support; forming a first source terminal, afirst drain terminal, and a first layer or body of semiconductivematerial supported on the support, the first layer or body ofsemiconductive material providing a first semiconductive channelconnecting the first source terminal to the first drain terminal;forming a first layer or body of dielectric material over the firstlayer or body of semiconductive material; forming a layer or body ofconductive material over the first layer or body of dielectric material;forming a second layer or body of dielectric material over the layer orbody of conductive material; forming a second layer or body ofsemiconductive material over the second layer or body of dielectricmaterial; patterning the first and second layers or bodies ofsemiconductive material, the first and second layers or bodies ofdielectric material, and said layer or body of conductive material touncover portions of the first source and first drain terminals andproduce a stack comprising the first semiconductive channel, a portionof the first layer or body of dielectric material over said firstchannel, a portion of the layer or body of conductive material over saidfirst channel, a portion of the layer or body of second dielectricmaterial over said first channel, and a portion of the second layer orbody of semiconductive material over the first channel; forming at leastone further layer or body of dielectric material over the stack to coverthe stack and said uncovered portions of the first source and drainterminals; patterning the at least one further layer or body ofdielectric material to form first and second windows through the atleast one further layer or body of dielectric material to said portionof the second layer or body of semiconductive material; and forming asecond source terminal comprising conductive material at least partiallyfilling the first window, and a second drain terminal comprisingconductive material at least partially filling the second window, suchthat said portion of the second layer or body of semiconductive materialprovides a second semiconductive channel, connecting the second sourceterminal to the second drain terminal, whereby the first FET comprisesthe first source terminal, the first drain terminal, the first channel,and said portion of the layer or body of conductive material, the secondFET comprises the second source terminal, the second drain terminal, thesecond channel, and said portion of the layer or body of conductivematerial.